I am generally happy with my installation of Loki but I have ran into a few bugs. The most confusing one is that, sometimes (not always, although I cannot predict when it will and will not happen), after I login it will just show my background for several minutes before the panel and dock load, if at all. Other times, both will load quickly, within a few seconds. I have a similar issue with shutting down occasionally too. Sometimes I will shut down and it will take about 5 minutes just stuck on the black screen with the elementary logo.
I have used Freya and I did not run into anything like this, though there were some driver issues which, thankfully, don't appear to have persisted with Loki. I'm running Loki on a Thinkpad T420 with 2 hard drives, 1 250GB SSD and a 500GB HDD. I have 16GB of RAM and an i5 processor clocking at 2.5GHz, so I do not believe that it's a problem with the processor or RAM.
I'm not sure if the problem could have been caused by my partitioning scheme, which is irregular: I have a 2Gb boot partition, a 22GB Root partition, and a usr and a usr/local partition taking up all of the space on my 250GB SSD. The 500GB HDD contains my Home Partition and 19GB of Swap. I partitioned my drives to try prioritise speed whilst having sufficient space for file storage.